If you're prompted for an update online, it will be direct from Mozilla. Which will not match the layout used by Vector Linux, and may be built against different deps.

In future, you would be better off saying no to any such update and using Gslapt to install the latest Vector package. They are usually pretty well up to date. Keep an eye on releases in the VL package news and updates section of the forum. New packages are announced there, and once an announcement is made, you will be able to enable the testing repo and install them. While not guaranteed to be safe, testing packages should at least allow you an easy way to remove a package which does cause you problems. You'll also be able to help testing new packages for Vector.